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A comparative study on the structural behavior of concrete arch dams subjected to swelling due to aggregate sllica reactions
South Africa is considered a water-scarce country and this fact alone stresses the absolute need to preserve its water resources. As time goes by, the ageing of dams in South Africa is becoming an increasingly important factor to consider from a dam safety perspective. When considering concrete dams...
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| Format: | Thesis |
| Language: | English |
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Department of Civil Engineering
2019
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| _version_ | 1867614332816195584 |
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| access_status_str | Open Access |
| author | Stehle, Hermann Theodor |
| author2 | Moyo, Pilate |
| author_browse | Moyo, Pilate Stehle, Hermann Theodor |
| author_facet | Moyo, Pilate Stehle, Hermann Theodor |
| author_sort | Stehle, Hermann Theodor |
| collection | Thesis |
| description | South Africa is considered a water-scarce country and this fact alone stresses the absolute need to preserve its water resources. As time goes by, the ageing of dams in South Africa is becoming an increasingly important factor to consider from a dam safety perspective. When considering concrete dams, Alkali Aggregate Reactions (AAR) which is the collective term referring to the potential chemical reactions between the cement and the coarse aggregate in the concrete, are a major cause of ageing. AAR causes internal swelling of concrete leading to stresses that eventually manifest on a macroscopic level as inter alia cracks, deformation and opening of horizontal construction joints. Although the effect of AAR expansion on arch dams is complex, certain behavioural phenomena have been identified as typical indicators of swelling concrete. These are well covered by literature. This thesis aims to compare the structural behaviour of concrete arch dams in South Africa that are subjected to swelling due to AAR. Three arch dams, namely Hartebeeskuil Dam, Poortjieskloof Dam and Thabina Dam (all located in different climatic regions), were identified and their behavioural patterns were investigated by using visual techniques along with the interpretation of instrumentation results. The typical instrumentation results that were used for interpretation purposes included geodetic surveying results, crack width gauge results, in situ stress measurement results and trivec measurement results. Poortjieskloof Dam, the oldest of the three dams, showed permanent upstream displacement trends of both flanks, but the centre of the arch showed a downstream displacement trend. Both flanks show swelling towards the abutments and rising crest levels are evident throughout the length of the dam wall. The dam wall was cracked quite severely on the downstream face and the horizontal joints showed clear separation. The most recent displacement trends suggest that the rate of AAR is decreasing. Hartebeeskuil Dam, the second oldest of the three dams, showed permanent upstream displacement trends throughout the length of the dam wall. Both flanks show swelling towards the abutments and crest levels at both flanks show some settlement. The central section of the arch show rising crest levels. The results of in situ stress measurements carried out in 1999 showed that the downstream section of the arch is experiencing tensile stresses while the upstream section of the arch is mostly experiencing compressive stresses. The cracking patterns on both the upstream and downstream faces seem to agree with these findings. The results generally seem to suggest that the AAR mainly occurs on the upstream side of the arch and that the effective arch has become thinner due to the tension zone on the downstream side. The most recent displacement trends suggest that the rate of AAR is not showing any signs of decreasing. Thabina Dam, the youngest of the three dams, showed permanent upstream trends of the right flank while the central region and left flank of the arch showed downstream trends. The flanks have moved permanently towards each other and the crest levels have increased throughout the length of the arch section. The most recent trends show increasing rates of strain especially in the vertical (z) and tangential (y) directions. More recently the entire arch has started showing upstream displacement trends. These may indicate the onset of a swelling mechanism in the concrete, most likely AAR, but extensive testing is required to prove this. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/29282 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:50:22.159Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2019 |
| publishDateRange | 2019 |
| publishDateSort | 2019 |
| publisher | Department of Civil Engineering |
| publisherStr | Department of Civil Engineering |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/29282 A comparative study on the structural behavior of concrete arch dams subjected to swelling due to aggregate sllica reactions Stehle, Hermann Theodor Moyo, Pilate Civil Infrastructure Management and Maintenance South Africa is considered a water-scarce country and this fact alone stresses the absolute need to preserve its water resources. As time goes by, the ageing of dams in South Africa is becoming an increasingly important factor to consider from a dam safety perspective. When considering concrete dams, Alkali Aggregate Reactions (AAR) which is the collective term referring to the potential chemical reactions between the cement and the coarse aggregate in the concrete, are a major cause of ageing. AAR causes internal swelling of concrete leading to stresses that eventually manifest on a macroscopic level as inter alia cracks, deformation and opening of horizontal construction joints. Although the effect of AAR expansion on arch dams is complex, certain behavioural phenomena have been identified as typical indicators of swelling concrete. These are well covered by literature. This thesis aims to compare the structural behaviour of concrete arch dams in South Africa that are subjected to swelling due to AAR. Three arch dams, namely Hartebeeskuil Dam, Poortjieskloof Dam and Thabina Dam (all located in different climatic regions), were identified and their behavioural patterns were investigated by using visual techniques along with the interpretation of instrumentation results. The typical instrumentation results that were used for interpretation purposes included geodetic surveying results, crack width gauge results, in situ stress measurement results and trivec measurement results. Poortjieskloof Dam, the oldest of the three dams, showed permanent upstream displacement trends of both flanks, but the centre of the arch showed a downstream displacement trend. Both flanks show swelling towards the abutments and rising crest levels are evident throughout the length of the dam wall. The dam wall was cracked quite severely on the downstream face and the horizontal joints showed clear separation. The most recent displacement trends suggest that the rate of AAR is decreasing. Hartebeeskuil Dam, the second oldest of the three dams, showed permanent upstream displacement trends throughout the length of the dam wall. Both flanks show swelling towards the abutments and crest levels at both flanks show some settlement. The central section of the arch show rising crest levels. The results of in situ stress measurements carried out in 1999 showed that the downstream section of the arch is experiencing tensile stresses while the upstream section of the arch is mostly experiencing compressive stresses. The cracking patterns on both the upstream and downstream faces seem to agree with these findings. The results generally seem to suggest that the AAR mainly occurs on the upstream side of the arch and that the effective arch has become thinner due to the tension zone on the downstream side. The most recent displacement trends suggest that the rate of AAR is not showing any signs of decreasing. Thabina Dam, the youngest of the three dams, showed permanent upstream trends of the right flank while the central region and left flank of the arch showed downstream trends. The flanks have moved permanently towards each other and the crest levels have increased throughout the length of the arch section. The most recent trends show increasing rates of strain especially in the vertical (z) and tangential (y) directions. More recently the entire arch has started showing upstream displacement trends. These may indicate the onset of a swelling mechanism in the concrete, most likely AAR, but extensive testing is required to prove this. 2019-02-05T06:40:24Z 2019-02-05T06:40:24Z 2018 2019-01-31T12:36:39Z Master Thesis Masters MSc (Eng) http://hdl.handle.net/11427/29282 eng application/pdf Department of Civil Engineering Faculty of Engineering and the Built Environment University of Cape Town |
| spellingShingle | Civil Infrastructure Management and Maintenance Stehle, Hermann Theodor A comparative study on the structural behavior of concrete arch dams subjected to swelling due to aggregate sllica reactions |
| thesis_degree_str | Master's |
| title | A comparative study on the structural behavior of concrete arch dams subjected to swelling due to aggregate sllica reactions |
| title_full | A comparative study on the structural behavior of concrete arch dams subjected to swelling due to aggregate sllica reactions |
| title_fullStr | A comparative study on the structural behavior of concrete arch dams subjected to swelling due to aggregate sllica reactions |
| title_full_unstemmed | A comparative study on the structural behavior of concrete arch dams subjected to swelling due to aggregate sllica reactions |
| title_short | A comparative study on the structural behavior of concrete arch dams subjected to swelling due to aggregate sllica reactions |
| title_sort | comparative study on the structural behavior of concrete arch dams subjected to swelling due to aggregate sllica reactions |
| topic | Civil Infrastructure Management and Maintenance |
| url | http://hdl.handle.net/11427/29282 |
| work_keys_str_mv | AT stehlehermanntheodor acomparativestudyonthestructuralbehaviorofconcretearchdamssubjectedtoswellingduetoaggregatesllicareactions AT stehlehermanntheodor comparativestudyonthestructuralbehaviorofconcretearchdamssubjectedtoswellingduetoaggregatesllicareactions |